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GABA A and glycine receptors in regulation of intercostal and abdominal expiratory activity in vitro in neonatal rat
Author(s) -
Iizuka Makito
Publication year - 2003
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2003.042689
Subject(s) - bicuculline , picrotoxin , strychnine , gabaa receptor , glycine receptor , chemistry , brainstem , anesthesia , gaba receptor antagonist , antagonist , medicine , receptor , endocrinology , glycine , biochemistry , amino acid
The roles played by GABA A and glycine receptors in inspiratory‐expiratory motor co‐ordination and in tonic inhibitory regulation of expiratory motor activity were studied using brainstem‐spinal cord (‐rib) preparations from neonatal rats. Inspiratory activity was recorded from the C4 ventral root. Expiratory activity in internal intercostal muscle, internal oblique muscle or T13 ventral root was evoked by a decrease in perfusate pH from 7.4 to 7.1 (i.e. from normal to low pH conditions) and was limited to the first part of the expiratory phase. Under low pH conditions, bath application of 10 μ m bicuculline, a GABA A receptor antagonist, caused the inspiratory burst to overlap the expiratory burst in 2/7 preparations. Overlapping of the expiratory burst with the inspiratory burst was observed in 7/7 preparations made under 10 μ m bicuculline. Furthermore, such preparations exhibited expiratory bursts under bicuculline‐containing normal pH conditions. Local application of 10 μ m bicuculline to the brainstem under normal pH conditions evoked expiratory bursts, some of which overlapped the inspiratory bursts. Picrotoxin, another antagonist of the GABA A receptor, had similar effects. Under normal pH conditions, application of strychnine (0.2‐ 2.0 μ m ; a glycine receptor antagonist) to the brainstem did not evoke expiratory bursts. On subsequent application of strychnine‐containing low pH solution, expiratory bursts were evoked and some (0.5 μ m ) or all (2.0 μ m ) of these overlapped the inspiratory burst. Simultaneous application of picrotoxin and strychnine to the brainstem evoked expiratory bursts that overlapped the inspiratory bursts and a subsequent decrease in perfusate pH to 7.1 increased the frequency of the respiratory rhythm. It was a characteristic finding that the duration of the expiratory burst exceeded that of the inspiratory burst under control low pH conditions. This remained true during concurrent blockade of GABA A and glycine receptors. The results suggest that in the in vitro preparation from neonatal rats: (1) GABA A and glycine receptors within the brainstem play important roles in the co‐ordination between inspiratory and expiratory motor activity, (2) tonic inhibition via GABA A receptors, but not glycine receptors, plays a role in the regulation of expiratory motor activity and (3) inspiratory and expiratory burst termination is independent of both GABA A and glycine receptors.